Process for removing acids from oils



Nov. 17, 1925.

P. w. PRu'rzMAN ET AL,

PROCESS FOR REMV-ING ACIDS FROM OILS Filed sept. 2, 1922 Clar Se/Hl'ng fami Zi? Ven @275' E 196m/ fruman.

Patented Nov. 17, 1925.

UNITED STATES 1,5uz,uuu

PATENT OFFICE.

PAUL W. PRUTZMAN AND PAUL D. BARTON, OF LOS ANGELES, CALIFORNIA, AS-

SIGNORS TO GENERAL PETROLEUM CORPORATION, OF LOS ANGELES, CALFORNIA,

A CORPORATION 0F CALIFORNIA.

PROCESS FOR REMOVING ACIDS FROM OILS.

Application filed September 2, 1922. Serial No. 588,040.

T0 all whom t may conce/rfa.'

Be it known that PAUL 1V. PnU'rzMAN and PAUL D. BARTON, citizens of the United States, residing at Los Angeles, in the county of Los Angeles and State of California, have invented certain new and useful Improvements in Processes for Removing Acids from Oils, of which the following is a specification.

The hereinafter described invention relates to a method treatment for acid treated oils generally, and for the purification thereof, although the same is more pt irticularly adapted for use in connection with the treatment of mineral lubricating oils and for the removal therefrom of the tarry ingredients and the dark-colored constituents thereof, and one of the objects of the invention is to carry out the treatment of oils for this Durpose at a less cost for the material employed in the treatment thereof, with less labor and with less fuel than has heretofore been required in the treatment of such oils.

A further object of our invention is to produce from an acid-treated mineral oil either a commercially neutral or an absolutely neutral finished product, without making use of any alkaline substance to neutralize the acidity, thus avoiding` the formation of any objectionable soaps, salts, or other ingredients.

A further object of our invention is to effect the neutralization of an acid oil without the darkening of color which, in the ordinary methods of treatment, arises in the re-solution of floating acid tar by the neutralized oil.

Then such mixtures of hydrocarbons and other bodies as occur in raw lubricating distillates from petroleums are treated with strong sulfuric acid in the manner commonly practiced, the acid reacts with certain constituents of the oil and forms with them a thickly viscid mass commonly called acid tar.

As the acid and the oil are, to a large extent at least, mutually insoluble, they are intimately mixed to promote reaction, usually by means of an air blast. The acid is thus brought into the state of a temporary emulsion in the oil, and this condition is maintained, but continuance of the agitation, until the acid expended its available energy,

lVhen agitation is discontined the acid tar is left floating in the oil in which, underthe conditions then obtaining, it is practically insoluble. The coarser particles soon subside, being materially heavier than the oil, collect into a semi-fluid mass, and may be withdrawn. rllhe finer particles subside very slowly, particularly from heavy and viscous oils, and it is rarely possible to allow the acid oil to rest long enough to allow these line particles to settle out completely.

The acid tar is, as said,- essentially insoluble in the oil, but only so long as it contains an excess of acid. If any body having the property of either neutralizing or dissolving the acid, such as an alkali or alkaline earth, an alkaline solution, or even a material proportion of water, be mixed with the oil in which the fine tar is suspended, the excess of acid which renders the tar particles essentially .insoluble in oil will be withdrawn from such particles by the alkali or Water, and the tarry portion of the particle will thereby be rendered quite freely soluble in the oil, particularly at temperatures somewhat above normal.

As the acid tar is a deeply colored body, having a high tinctorial value, re-solution of tar may and usually does seriously depreciate the color of the oil; and as this tar contains the impurities withdrawn from the oil by the acid treatment, as well as others formed by the action of the acid on certain other elements of the oil, re-solution of tar causes the oil to be contaminated with the very impurities Which it is the object of the acid treatment to remove.

After application of sulfuric acid to mineral oils followed by complete removal of the tar, the oil is still left in an acid condition. This acidity is due to the presence of free sulfuric acid mechanically held, to organic compounds such as sulfonic acids and alkyl sulfuric acids, which are often more soluble in oil than in either tar or water, and in many cases to certain bodies existing in the raw material, having the properties of acids, and known as petroleum acids or naphthenic acids.

All these acids except possibly the naphthlenic acids are reactive to metals, causing corrosion, and therefore cannot be left in the finished lubricating oil. Further, they are unstable to air and light and if allowed to remain, even in slight traces, will cause. the oil to darken in color and acquire an unpleasant odor, by either of which changes its commercial value is much lessened.

To destroy these acid bodies .it is cus tomary to add to the oil and alkaline solution, usually of caustic soda, by which the acids are neutralized. That is to say, they are converted into sodium salts, many ot which salts are viscid, stringy liquids quite similar in appearance and behavior to the potash soaps ot the higher fatty acids.

Thesel salts or soaps were long supposed to be completely soluble in water, and also to be harmless if small proportions were left behind on washing the oil with water. lt is now recognized that they are only partly watel1 soluble, so that water washing' can never remove them completely, and also that remaining traces too small to etlfect the appearance ot the oil are highly deleterious to its quality.

To effect the removal Lfrom the oil oit these sodium salts it is customary to wash the oils With water, by adding to the batch successive doses of water, mixing each dose with the oil until it has taken up a portion of the Water-soluble elements, then allowing the water to subside and withdrai'ving it, This process is repeated until no further solution oi salts can be had, and the water settles out clear and bright.

lllashing is liable to be a difficult and tedious operation, particularly if the oil be very viscous or the proportion of salts in thc oil be large. This difficulty is founded in the soapy nature et some ot the sodium salts, which causes them to act etiicient emulsifying agents, so that the wash waters often settle out slowly, and in settling entrain and carry away a considerable proportion of the oil itself. ln extreme cases the entire mass of oil, soap and water forms a permanent emulsion, which cannot be prolitably separated, and in such cases the cost oit treatment ot the batch is lost.

Again, in 'atei' washing after neutralizH ing with an all-rali, only such portions ot the salts as are more soluble in water than in oil can be removed, Thus such salts as are more soluble in oil than in water (and these are almost always present) are lett behind, yielding a linished oil prone to emulsily with water, and having a high ash content.

Again, if an excess ot strong alkali be used, or if the proportion ot sodium sul fate in the neutralization product be high, the alkali or the salt, as the case may be, will often salt out the soapy bodies in a form in which they are soluble in neither water nor oil. lts this rejected ina s the consistency ot soi't soap, the tig and most resistant emulsion possible is often formed.

Again, when a large. proportion of water is added to a solution ot an organic salt or soap, hydrolysis takes place, with separation of a variable proportion ot such salt into its original constituents, viz: an acid body and an alkaline body. ln such cases the allaline body remains in solution in the water, while the acid body lasses back into solu tion in the oil. lt is not only possible, but is actually a very common occurrence, to obtain an oil having an acidity too high for certain uses, even after repeated Washings with alkaline waters.

Under our invention depreciation ot color by re-solution ot acid tar; the cost of long` continued water washing; the loss of o-il incident to partial einulsitication during washing; the danger ot complete emulsiticaton during washing; and the likelihood ot irremovable acidity in the iinishcd product are avoided by substituting 'lor alkali and wash waters the use ot' certain clays and other solid adsorbent .materials which, with out themselves reacting with these bodies, may be made the means by which the floating tar and the dissolved acidity are taken up. On subsequent removal ot the solid material, by sedimentation or liltration or other mechanical means, the tar and the acid bodies are removed alongl with the solid material in and on which they are lined, ',lhe `purified oil is thus left clean, brilliant, neutral, tree from soaps or salts, resistant to en'mlsiication, and with a very low ash content.

The power ot adsorbing acidity from oils is a specific property oi many clays and other adsorbent solids. its existence may be discovered and its value determined by preparing a sample ot acid oil, 'freeing this sample trom lar, determining the acidity oit the tar-tree oil by titration with an alkaline solution o t known strength, adding a sample ot the tinely ground adsorbent, warming the oil until limpid, stirring 'tor several minutes, filtering out the clay or other adsorbent used, and again determining the atridit,r ot the oil by titration. lt the acidity ot the oil attrib the clay application is less than it was betere such application, then the clay or other adsorbent has the propertyY ol ad sorlriing` zuidity, and is suited `tor use in the carrying out ot our invention.

it will be obvious that it the above test is carried out with weighed quantities oi matcrials the attsorption ol acidity may be reduced to a numbe f, as ior instance, the equiv alent in milligra ,is ot potassium hydrate per gram ol adsorbent tal-Ien. By this means the relative values for this purpose ot various clays and other adsorl compared.

Tilarieus adsorl for the purpose many natural cla,

'"ls may be t our invention, includn c s and particularl;` such as llt) lil?

.iso

are classed as Ftloridins or decolorizing clays, the mineral bauxite, the mineral halloysite, the mineral ot'aylite or montmorillonite, and the residues resulting` from the sulfuric acid treatment ot the above minerals. Light adsorbent bodies, such as the animal and vegetable chars, are not suited to use in this process as they do notv settle readily enough. Clays or other minerals containing,l any notable alkalinity, if this alkalinity is in a form readily reactive With sulfuric acid, are not suited tor use in this process, as they are likely to produce salts with the acid bodies in the oil, Which salts may remain in the oil to deteriorate its quality. 1

lt Will be understood that Where the terni adsorbent is used herein We roter to a powdered solid substance, having:r the property ot adsorbing acidity trom an oil previously treated with sulfuric acid, and essentially free from substances which react with small quantities ot Weak sulfuric acid to form mineral salts.

To secure the best results under our process the adsorbent should be ground to a powder, but not ot the tinest grain. rihe rule is that finer grinding `@gives more rapid adsorption of acid bodies and slower settling mirom the oil7 and the best tineness is that at which these two properties are so balanced as to allow the total effect to be had in the minimum ot time. The most desirable fineness in most cases is that at Which the porvder vvill pass completely through a standard 100 mesh sieve and be completely retained on a standard 20() mesh sieve. rl`his grade ot powder is ol'ten diilicult and expensive to prepare and a powder passing completely through a 100 mesh sieve only is an approved `grade for the purposes ot this invention. Even .less .finely ground powders may be used, though to less advantage, and the mesh above specified is a preferred grade only.

In the carrying,l out our method invention ive apply the clay to the oil in a number ot small doses, removing each dose by settling it and decanting the oil betere adding the next. This dos f is continued until the acidity is comple ely removed from the oil, or until it is reduced to the allowable minimum fixed by the use to 'which the oil is to be put. The clay doses are not discarded after once using, but are applied to successive quantities et oil each more highly acid than the one pro edng it` and iinally to a quantity ot nov.' acid oil containing the maximum proportion oi acidity and also any ioating tar which may remain trom the acid treatment of the cil. By this means a cycle ot operations is set up, in which as the acidity ot' the oil is decreased it is .brought into contact With successive quantities ot less and less saturated adsorbent, while the clay doses as they adsorb acid and decrease in adsorptive value are brought progressively into contact with successive quantities of oil of increasing acidity. Thus, what might be termed al head or potential of acidity concentration is maintained against the clay, and by this means the clay .is enabled to adsorb all the acidity from the oil and at the same time to become itself satura ed With adsorbed acids.

Any suitable apparatus may be employed for the carrying out ot our method invention, a simple effective andlpractical appa.- ratus being` shown in the accompanying' drawing, wherein the reference letters A, B, C, D and E are digesters,y in which oil and adsorbent are mixed. R is a settling' tank into Which the spent adsorbent is discharged ior the purpose ofrecovering' a portion ot the oil contained therein. F is the storage tank for the oil prior to the treatment by the present process. G is a pump by means of Which acid treated oil is transferred from .F to any one ot' the tive digesters. H, I, J, K and L are pumps, preferably of the centrifugal type, by means of Which the liquid contents otl each ot' the digesters may be transferred to either of the tWo digesters next to it in the cycle, thus: A to B or C, B to C or D, C to I) or E, D to E or A, and E to A or B. M, N, O, P and Q, are pipes through which the adsorbent, after subsiding to the bottom of the digesters, may be draivn to the settling tank R. S is a tank into which the finished product, still containing some suspended clay, is discharged tor storage prior to liltration or other process ot' removal ot such suspended matter.

'To start the operation and set up the cycle it is necessary to use new clay and to proceed in the followingmanner.

Digester A is filled With acid oil from F. and a clay dose sutlicient to agglon'ierate and knock down the tar is added. rIhe batch is then thoroughly mined, by circulating,` through pump H, or by means of any suitable mixing;` device not shown` Within the digester. A screiv propeller set close to the point of the cone ot'` the dieester, and arranged to operate at high speed, is a preferred type ot mechanical aeitator for this purpose. An air blast may be used instead of a mechanical agitation, but is less desirable, as the linal product will have a poorer color and the clay doses will settle less rapidly. lVhatever n'ieans oi agitation is used, agitation is continued until the tar is thoroughlyagglomerated into relatively coarse grains by adhesion to the clay grains and by the adhesion of such particles to each other. 1When this point is reached the clay and tar will settle readily from the oil, leaving` it essentiaily clear but of a very dark color. 1f the oil is viscous it may be heated, but the lowest possible temperature should be used, as While a higher temperature accele 'ates the operation it is liable to cause re-solution of the tar if applied to an oil not ali'eady freed from most of its acid. It should not be necessary to heat over 1000 Fahr. with an ordinary oil, and such heat should be applied as gently possible, by means of immersed coils heated by lon pressure steam, or preferably by means of an exhaust steam or Warm air jacket.

As soon as the oil is freed from tar as above described the agitation is interrupted, and the clay and tar allowed to settle. llllien the solid content has settled to a sharp line, the supernatant oil is transferred througl'i lpump H into din'ester B, and the slush of clay, tar and oil is d ai'n through pipe 'Il into settling` tanl; B.

Then the pumping from fr to B is conipleted, A is refilled With acid oil from F,

and each digester is given a dose of nen' clay. mixed and settled as befo 'e.

The oil from direeter l5 is non' pumped olf into C, leaving' the clay behind. The oil from n is pun'ipeil into f3 on top of the clay remaining there. The clay slush is drawn from A into tank R, and n is refilled with fresh acid oil from F. Xie and C are given fresh clay doses, and the three dieesters are mixed and settled as before.

The oil from digester C is now pumped olf into l), leavin;` the clay behind. The oil from B is pumped olf into C, leaving' the clay behind. The oil from A is pini-'ipod o'i" into E, the clay slush is d ann from A into tank R, and i is refilled nith fresh acid oil from tank F, .f h doses, and the four diejesters are settled as before.

The oil in eiester D l doses of clay, and we -will tration that the dose has .h tioned that this number is sriiicient to the treatment and yield a neutral oil, oil in this iligg'ester is therefore pumped into tanl S, from which it is taken to hare the last traces of clay reinored by iiltration or other convenient manner. 'lhe oil in digester (l is nonY pumped into lil: .it has had three di s of clay. and is given a .fourth dose of nenv clay in E. The oil in di;7 ter B has had tiro denses of clay, and is pumped on top of the clay remaininur in l), which has been applied to one batch of oil. The oil in digesler [it has had one dose of el' y. and is pumped on iop of the clay remaining' in (l. which has been applied to tiro batches of Digester l .is refilled with fi li acid from l?. on top of the clay remaining in B, which has been applied to three hatches f he clay reinaininf;` in A, which lr it. and l) are einen frcs' mixed and f oil.

hee i applied to i batch coi ta is i se ess and is drawn don'n i tanl; l.

The full cycle of operation nonv estatlished` and their h,ter the or t' 'l'elOH- pumping, intreducingv ne y oil and f Leoben 'and it is ingv and settling repeatthemselves indefinitely. For instance, after the next mixing and Settlingl following the last operation described aboye, the oil in digester E is pumped out of the cycle, into tank S. The oil in digester D has had three doses, and is pumped into the empty dig-jester ifi to be given a. new dose. The oil in digester C lrs had tn'o clay doses and is pumped into ll on top of clay which has been on fr cycle of four doses is given nay of illustrationx and be lanse it is a orally useful and desirable number but goed results may be had by using` a lgreater or number. In any case, as will be shown by the exaniination of the cycle merely by gendoses,

just stated, only one dose of new clay is added to the cycle for each batch of new oil added, so that a single dose of clay, though it takes acidity from four different batches of oil, has to take up in total just the amount of acidity originally present in one batch of fresh oil, so that the size of the clay dose is determined by the capacity of the clay and the amount of acidity present .in one ln tch of oil, While the most favorable number of doses is the smallest number with which the clay cz n be completely satin 'rt rl in its progress through the cycle, so that none of its capacity shall be lost. Giyen complete saturation of the clay` a larger number of doses merely increases the aniount i lt will be understood tha: the number of doses of adsorbent, the tennlrierature at which they a re plied, and the forni of appa latus shown. a

Le for illustrative purposes only iot ou intent or desire to be understood as linitingrlY or re ,rictn'ig the .invention to the particular nietliaiii steps hereinliefore set inth. inasmuch as the spirit of our in- Ventron hes or resides in tl ie application to an acid eil of a plurality of doses )f edf sent, and in tl a ication of each dose ity :f quantities of `i of the UnitedStates, is:- inetnod et utilizing an adsorbent from tar-containing as Len* and desire to protect by lll) which consists in tbe agitation with suoli oil of a powdered adsorbent, which adsorbent has previously expended its adsorptive value in removing` impurities from tar-free oils and is charged with said tar-free oil.

In testimony whereof We have signed our names to this specification.

PAUL lV. PRUTZMAN. PAUL D. BARTON. 

